ninja tool sometimes obscures getting file contents for scanning

[mwichmann]

This information is collected from the discord thread at https://discord.com/channels/571796279483564041/1262451038435414027 Filing this to make sure it's captured, I did not discover it.

It is reported that sometimes dependencies are not found when generating the build.ninja file. This appears to happen because the tool monkey-patches several core SCons routines as not needed, so the ninja work can go faster. One of those has a side effect that may not be what we want:

    SCons.Node.FS.File.get_contents = ninja_contents(SCons.Node.FS.File.get_contents)

Means for a File node, we get a decorated form of get_contents. The decorator is:

def ninja_contents(original):
    """Return a dummy content without doing IO"""
    def wrapper(self):
        if isinstance(self, SCons.Node.Node) and (self.is_sconscript() or self.is_conftest()):
            return original(self)
        return bytes("dummy_ninja_contents", encoding="utf-8")

    return wrapper

So only if the node is an SConscript file, or we're a conftest node will the file's contents be returned, else it's skipped. That's fine - we don't need the binary file contents in ninja mode, but we do need the text contents, for use by the scanner, if the file type has a scanner. There is no consistency about how this is done across all the Node types, but in the case of File nodes, get_text_contents is implemented in terms of get_contents:

    def get_text_contents(self) -> str:
        """Return the contents of the file as text."""
        return SCons.Util.to_Text(self.get_contents())

Since the matching get_contents is stubbed out in this case, we don't get any file contents. Most scanners use get_text_contents, so perhaps some rethinking is needed here.

Some code permalinks:

• https://github.com/SCons/scons/blob/731337725b2ccf668c7187072328faa57ff8c144/SCons/Tool/ninja/init.py#L391C1-L391C86
• https://github.com/SCons/scons/blob/731337725b2ccf668c7187072328faa57ff8c144/SCons/Tool/ninja/Utils.py#L388
• https://github.com/SCons/scons/blob/731337725b2ccf668c7187072328faa57ff8c144/SCons/Node/FS.py#L2739